Vacuum interrupter contacts

ABSTRACT

The contacts of the arrangement are employed in a vacuum interrupter and include discrete bodies of copper and titanium sintered or laminated together. It is old in the art to employ a copper and titanium alloy in such contacts. However, it has been discovered that the use of a sintered or laminated structure increases the thermal and electrical conductivity of the contacts from about 17 to 90 percent of that of pure copper. The titanium still retains its desirable property of preventing contact welding. It also acts as an unusually good getter. The conductivity increase, however, affords substantial additional advantages. Switching efficiency is improved by a higher electrical conductivity. Higher electrical conductivity also reduces heat generated by the passage of current through the contact resistance. Arc suppression is, thus, enhanced when the switch is turned off. A higher thermal conductivity also helps in arc suppression because the heat caused by the arc and current passing through the contact resistance is quickly conducted away.

United States Patent Continuation of application Ser. No. 837,124, June 27, 1969, now abandoned. This application Mar. 18, 1971, Ser. No.

[54] VACUUM INTERRUP'IER CONTACTS 9 Claims, 3 Drawing Figs.

[52] US. Cl. 200/166 C, 75/208 [5]] lnt.C|. 01h 1/02 [50] Field 01 Search 200/l66 C, 144 B; 75/208. 222; 29/1822 [56] References Cited FOREIGN PATENTS 693,827 9/1964 Canada 200/ 144 B Primary ExaminerH. 0. Jones Attorneys-C. Cornell Remsen, .lr., Walter J. Baum, Paul W. l-lemminger, Percy P. Lantzy and Thomas E. Kristofferson ABSTRACT: The contacts of the arrangement are employed in a vacuum interrupter and include discrete bodies of copper and titanium sintered or laminated together. It is old in the art to employ a copper and titanium alloy in such contacts. However, it has been discovered that the use of a sintered or laminated structure increases the thermal and electrical conductivity ofthe contacts from about 17 to 90 percent of that of pure copper. The titanium still retains its desirable property of preventing contact welding. It also acts as an unusually good getter. The conductivity increase, however, affords substantial additional advantages. Switching efficiency is improved by a higher electrical conductivity. Higher electrical conductivity also reduces heat generated by the passage of current through the contact resistance. Arc suppression is, thus, enhanced when the switch is turned off. A higher thermal conductivity also helps in arc suppression because the heat caused by the arc and current passing through the contact resistance is quickly conducted away.

VACUUM INTERRUPTER CONTACTS,

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation of copending application,

Ser. No. 837,124 which was filed June 27, I969 and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to switch contacts and, more particularly, to getter-containing, highly conductive contacts for vacuum interrupters.

In the past, it has been the practice to alloy a highly conductive metal such as copper with a gettering material such a titanium. For example, see U.S. Pat. No. 3,379,846.

The use of titanium as a getter is advantageous. However, the electrical and thermal resistance of a copper-titanium alloy is relatively high. This is disadvantageous because switching efficiency is thereby decreased. That is, more power is lost by current passing through the contact resistance. Further increases in electrical and thennal resistance causes an arc to be sustained when the switch is turned off. The current passing through the higher electrical resistance dissipates more heat which tends to sustain the arc. The higher thermal resistance prevents the heat of the are from being conducted quickly away from the arc.

SUMMARY OF THE INVENTION In accordance with the device of the present invention, the above-described and other disadvantages of the present invention are overcome by providing contacts of discrete bodies or particles of a highly conductive material and a getter.

By keeping the particles individually separate, it has been discovered that the contact electrical and thermal conductivity can be increased from about 17 to about 90 percent that of pure copper. The contact resistance, thus, is much lower than was the case with prior art contacts. The contacts of the invention, thus, have a high switching efficiency and a high arc-suppressing capability. These advantages are achieved because of the low electrical and thermal resistance. A lower power loss in the lower electrical resistance results in increased efiiciency. The reduced heat generated and the high thermal conductivity makes arc suppression possible.

The above described and other advantages of the invention will be better understood from the following description when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, which are to be regarded as merely illustrative:

FIG. I is a side elevational view, partly in section, of a vacuum interrupter;

FIG. 2 is a perspective view of apparatus employed in the manufacture of a vacuum interrupter contact in accordance with the present invention; and

FIG. 3 is a perspective view of contacts made in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings, in FIG. 1, a vacuum interrupter is indicated at 10. Vacuum interrupter has electrical contacts 11 and 12 silver or gold soldered or otherwise securely fastened to cylindrical copper posts 13 and 14, respectively. The entire construction of vacuum interrupter 10 may be conventional with the exception of the construction and composition of contacts 11 and 12.

Vacuum interrupter 10 includes an evacuated envelope 15 having copper rings 16 and 17 brazed between metal discs 50 and 51, and ceramic cylinders 52 and 53, respectively. Rod 13 is brazed to disc 50. A bellows I9 is fixed at one end to disc 51 and at its other end to rod 14. A metal shield 20 fixed between cylinders 52 and 53 prevents metal vapor from coating the interior of the envelope 15 and shorting out discs 50 and 51.

Contacts 11 and 12 may be made of a sintered mass of particles of two different metalssuch as copper and. titanium. Preferably, one metal is highly conductive, such as copper or silver. The other metal is preferably titanium, but may be any equivalent thereof. The titanium acts as a getter. Preferably, an active metal is employed for the getter. Active metals which may be used are incorporated in the following list.

Beryllium Magnesium Boron Silicon Cerium Thorium Chromium Titanium Columbium Yttrium Haflnium Zirconium Lamhanum Use of the metals below is preferred.

Beryllium Silicon Boron Thorium Columbium Titanium Hafnium Zirconium Lanthanum As stated previously, titanium is preferred above all.

According to one feature of the invention, contacts 11 and 12 are made as follows. IOO-mesh, oxygen-free, highly conductive (OFHC) copper particles are mixed with I00-mesh titanium particles, at least 99.5 percent pure, by weight. OFHC copper is of 99.99 percent purity and contains not more than 6 parts per million oxygen. The mixture is adjusted to contain about percent, by weight, of copper and about 10 percent, by weight, of titanium. Particles size of the powders is not critical and can be ZO-mesh or larger. To obtain a contact of low porosity, however, it is desirable to use powders of graded size in the manner well known to producers of sintered metal parts. The ratio of copper to active metal is not critical and may be varied at will to meet the particular switching application. In general, as little titanium is used as will getter residual gases when the contacts interrupt current and as will provide the required antiwelding properties. The percentages given, however, have been found satisfactory for the interruption of from 1,000 to 25,000 amperes of 60 Hz. power.

The mixture is compressed dry in a mold to form a unitary body of sufficient mechanical strength to hold itself together. Pressures are typical of those used in powder metallurgy, about 25 tons per square inch. The body may take the form of a wafer or button having flat, parallel upper and lower surfaces and a cylindrical side surface. The button so made, is then vacuum-sintered a few degrees below the eutectic. The eutectic temperature of copper and titanium is about 880 centigrade. The vacuum-sintering process is conducted under relatively high vacuum conditions of the order of 10' Torr to avoid contamination of the active metal. A common commercial grade of oxygen-free, highly conductive copper is preferably used. The contacts are then silver-soldered to posts 13 and 14 in a conventional manner.

An alternative method of making contacts 11 and 12 is illustrated in FIGS. 2 and 3.

In FIG. 2 a stack 21 of copper and titanium sheets is compressed between members 22 and 23 in a vacuum. A titanium sheet is placed between each adjacent pair of copper layers in Stack 21. The titanium sheets are 3 mils thick. The copper sheets are 25 mils thick. The stack 21 is heated in a vacuum below the eutectic until the stack 21 begins to yield. The layers of stack 21, then, form a diffusion bond therebetween. The pressure is immediately removed from the stack at the yield point and the stack cooled. Contacts 24 are then formed on a lathe and sliced as shown in FIG. 3.

The laminated contacts are then silver-soldered to posts 13 and 14 in the conventional way. Note will be taken that the laminations will run in a direction perpendicular to a plane through the axis of posts 13 and 14.

The ratio of metals can readily be varied by a change in relative thickness of the high-conductivity and active metal layers used to make the contacts. The exact metal thicknesses chosen will depend on many variables, for example, the cost and availability of the metals in various thicknesses and on the service to which the contacts will be put. The thicknesses given in the example, however, have been found satisfactory for the interruption of 60 Hz. current of 1,000 to 25.000 amperes.

Other metals obviously can be added if desired to either the powder or laminated contact before pressing. For example, small percentages of lead or bismuth can be added as additional antiweld agents. Tungsten or molybdenum can be added if desired to decrease the rate of contact erosion under arcing conditions.

What is claimed is:

l. A vacuum interrupter comprising: an evacuated envelope; support means in said envelope including a post of highly conductive material; and at least one electrical contact conductively affixed to an end of said post, said contact comprising a button formed of intermixed particles of a highly conductive material and particles of an active gettering material formed into a bonded mass which has been subjected to compression and heating to a point below the eutectic, thereby to prevent alloying and the formation of solutions of said gettering material in said highly conductive material.

2. The invention as defined in claim 1 wherein said post is composed of copper, said contact button is comprised of a compressed mass of said particles vacuum-sintered below the eutectic, said highly conductive material including copper of at least 99.99 percent purity, by weight, and comprising 90 percent of said particles, by weight, said gettering material being 99.5 percent pure titanium, by weight, and comprising the remaining percent of said particles, and all of said particles being approximately 100 mesh.

3. The invention as defined in claim 1 wherein said post of highly conductive material is copper, said contact includes a laminated button of alternate copper and titanium strips soldered to an end of said post, said strips lying in planes substantially parallel to a plane containing the longitudinal axis of said post, said copper strips being approximately 0.025 inch thick, said titanium strips being approximately 0.003 inch thick, and adjacent ones of said strips being diffusion bonded therebetween.

4. The invention as defined in claim 1, wherein said particles are formed into a molded, compressed mass, vacuum-sintered below the eutectic.

5. The invention as defined in claim 4, wherein said gettering material is one of a group consisting of:

Beryllium Magnesium Boron Silicon Cerium Thorium Chromium Titanium Columbium Yttrium Hafniurn Zirconium Lanthanum Beryllium Magnesium Boron Silicon Cerium Thorium Chromium Titanium Colum bium Yttrium Hafnium Zirconium Lanthanum 9. The invention as defined in claim 8, wherein said highly conductive material is copper. 

1. A vacuum interrupter comprising: an evacuated envelope; support means in said envelope including a post of highly conductive material; and at least one electrical contact conductively affixed to an end of said post, said contact comprising a button formed of intermixed particles of a highly conductive material and particles of an active gettering material formed into a bonded mass which has been subjected to compression and heating to a point below the eutectic, thereby to prevent alloying and the formation of solutions of said gettering material in said highly conductive material.
 2. The invention as defined in claim 1 wherein said post is composed of copper, said contact button is comprised of a compressed mass of said particles vacuum-sintered below the eutectic, said highly conductive material including copper of at least 99.99 percent purity, by weight, and comprising 90 percent of said particles, by weight, said gettering material being 99.5 percent pure titanium, by weight, and comprising the remaining 10 percent of said particles, and all of said particles being approximately 100 mesh.
 3. The invention as defined in claim 1 wherein said post of highly conductive material is copper, said contact includes a laminated button of alternate copper and titanium strips soldered to an end of said post, said strips lying in planes substantially parallel to a plane containing the longitudinal axis of said post, said copper strips being approximately 0.025 inch thick, said titanium strips being approximately 0.003 inch thick, and adjacent ones of said strips being diffusion bonded therebetween.
 4. The invention as defined in claim 1, wherein said particles are formed into a molded, compressed mass, vacuum-sintered below the eutectic.
 5. The invention as defined in claim 4, wherein said gettering material is one of a group consisting of: Beryllium Magnesium Boron Silicon Cerium Thorium Chromium Titanium Columbium Yttrium Hafnium Zirconium Lanthanum
 6. The invention as defined in claim 5, wherein said highly conductive material is copper.
 7. The invention as defined in claim 1, wherein said button are strips formed in a laminate with a diffusion bond between strips, one strip of a highly conductive material being positioned between each adjacent pair of strips of said gettering material, said strips running perpendicular to a plane through the axis of said contact.
 8. The invention as defined in claim 7, wherein said gettering material is one of a group consisting of: Beryllium Magnesium Boron Silicon Cerium Thorium Chromium Titanium Columbium Yttrium Hafnium Zirconium Lanthanum
 9. The invention as defined in claim 8, wherein said highly conductive material is copper. 